Three-dimensional polymer parts can be produced via photopolymerization processes. In one such photopolymerization process, a digital, three-dimensional model of the part to be created is produced. This model is digitally broken into cross sections. A fluid medium capable of altering its physical state when exposed to specified intensities and wavelengths of light is placed upon a planar transparent image plate. An exemplary fluid medium such as a photopolymer resin is exposed to patterns of light representing successive adjacent cross sections of the part being produced. This results in the creation of a hardened polymer layer in the desired shape, attached to the image plate. This layer is then separated from the image plate. Subsequent adjacent cross sections are produced in the same manner and automatically integrated together to provide a step-wise, cross-sectional assembly of the part. The part is drawn away from the substantially planar, parallel surfaces of the fluid medium and image plate. This and similar processes are also known as “3D printing” and hereinafter shall be referred to as such.
Layer-wise assembler devices such as 3D printers are used to rapidly and autonomously produce parts based on computer input. Some 3D printers are used to produce runs of identical parts in the tens, hundreds, or thousands. Other 3D printer applications allow designers to rapidly prototype. That is, the 3D printer enables a designer to create a physical prototype of a desired part that was first digitally created in a computer aided design program. This can then be used to examine the efficacy of the design in the real world. In the preceding examples, uniform, rapid production on the order of minutes is sought. 3D printing machines are designed with this design parameter in mind. Operators of 3D printing machines must constrain the design of parts being produced by the 3D printer in order to allow the machine to quickly produce quality parts. If a design is provided which is outside of the 3D printer's operating parameters, inconsistent parts may be produced.
When a cross-sectional layer is formed on the image plate, the newly-formed layer often adheres strongly to the image plate. Two types of forces prevent separation at the interface between the image plate and the newly-formed layer: (1) the adhesion force between the image plate and the newly-formed layer; and (2) a vacuum force present between planar objects in a fluid. The adhesion force is comprised of chemical bonding forces between the image plate and the newly-forced layer. In some aspects, the adhesion force also comprises mechanical adhesion forces between the image plate and the newly-formed layer. In order to separate the part from the image plate and continue assembling it, a separation force must be applied in order to overcome the adhesion and vacuum forces present.
Application of the separation force stretches and strains the part being formed in non-uniform, undesirable ways. In some 3D printers, the separation force is strong enough to distort or destroy fragile portions of a part because the fragile portion is stretched, strained, and even completely separated from the part as the construction plate and part are repositioned relative to one another in order to form the next layer of the part. Because this separation force destroys or damages fine detailing in a desired part design, the resolution of 3D printers has been limited. Parts containing, for example, very thin segments or intricate detailing (e.g., channels, tubing, and the like) cannot be produced, are produced with an extremely high failure rate, or must be produced at a very slow rate using different photopolymers in order to produce a part containing fragile sections that will not deform when exposed to the separation forces produced by the 3D printer.
Previous 3D printers have simply pulled the part away from the image plate. Application of significant separation force, however, causes the formed layer to be deformed or to break when the part is repositioned. Other approaches seek to minimize adhesion forces by applying an inert layer between the image plate and the newly-formed layer, such as the Teflon® material available from E.I. du Pont de Nemours and Company of Wilmington, Del. These approaches lessen the separation force by reducing adhesion forces, but do not mitigate the vacuum force.